exchange server (if its the regular Microsoft exchange) will only load on server..... a server setup in/as a domain... NT4 workstation, 2000 pro, xp home and pro will not support it and doesn't have the services it needs.

any version of ms exchange needs a domain already setup for it to be added to on load

It depends on what version of Exchange. If its Exchange 2000 you will need to setup active directory. If you do not know how to do this you need to read in the help files onhow to. It is not that complicated but it can be tricky.
Good Luck

Install the NT4 server and promote it to a DC, that's all you have to do. If you're running exchange 5.5 I recommend using NT4, but if you're using Exchange 2000, use Win2k for your domain. NT4 domains are much different from there succcessor (Win2k). If you were to run Exhange 5.5 on A Win2k box you would have to modify the Active Directory Schema, not a fun thing IMHO. Both the Exchange 2000 and Win2k use the LDAP protocol to access the directories... Ok I'm rambling on again